Factors Influencing the Distribution of Species of Californian Coastal Sage Scrub

Abstract

The distributions of species and species groups of southern coastal sage scrub in Alta and Baja California are examined in relation to structural and environmental variables. Variables examined include vegetative structure, geographic and topographic position, soil physical characteristics and macronutrient levels, substrate, temperature, precipitation, and factors of disturbance (fire, light grazing, air pollution). Evapotranspirative stress during summer months seems to be a major factor influencing species distributions. Mean temperature of the warmest month appears to be a better predictor of this stress than seasonal or annual precipitation levels. Many of the dominant species also respond sensitively to differences in soil fertility and parent material, with 18 of the 21 dominant species examined showing significant preference for a single substrate among seven classes. Among soil nutrients, levels of organic and nitrate nitrogen appear as particularly useful predictors of species distributions. Of disturbance variables, regional levels of air pollutants are correlated most strongly with floristic differences. Multiple linear regression equations are presented permitting prediction of species' foliar cover levels from levels of environmental variables. Geographic segregation of floristic associations within the sage scrub flora is most marked along a northwest-southeast axis paralleling the Pacific coastline, although southern inland (Riversidian) associations show affinities with the northern coastal flora. Medium-scale patchiness ( = 0. 1 ha) in floristic composition occurs within the sage scrub due to local dominance by one or a small number of shrub species. The possible ecological significance of this is briefly discussed.

Local patterns of diversity in California northern coastal scrub

“…Larger‐leaved species were observed more often in the mesic scrub group, and smaller‐leaved species were observed more often in the xeric scrub group. Additionally, elevation, slope, and aspect patterns in the data support the interpretation of water availability being a significant process (Cornwell & Ackerly, 2009; Franklin, 1998; Keeley & Keeley, 1988; Moody & Meentemeyer, 2001; Poole & Miller, 1981; Westman, 1981), as well as heat load (McCune & Keon, 2002), and thus potential evapotranspiration (PET) among sites at a fine scale. As a whole, in ordinations, mesic scrub plots were in opposition to plots in the xeric scrub group (Figure 5a,b).…”

“…One hundred and six rare or endangered plant taxa are associated with NCS vegetation, of which 79 are California endemics (Calflora, 2015; CNPS, 2015). Despite its floristic and physiognomic diversity and its recognition as a major shrubland formation of the CFP (Westman, 1981), relatively little formal study of NCS has occurred.…”

Reconstruction of the historical changes in mycorrhizal fungal communities under anthropogenic nitrogen deposition

“…These consequences may have already occurred within the Los Angeles Basin, but no historic record exists to enable us to evaluate the mechanisms of plant community change with nitrogen enrichment at San Dimas. Nevertheless, contemporary data suggest that such changes may have already occurred in southern California (Westman 1981;Minnich & Dezzani 1998) and elsewhere (Aber et al 1989;Schulze 1989;Fenn et al 1998) on a landscape scale and, hence, may foreshadow continuing changes in the industrialized world. Air pollution in Phoenix, Houston and Tucson may soon match the magnitude recorded within the Los Angeles Basin.…”

Plant water status and hydraulic conductance during flowering in the southern California coastal sage shrub Salvia mellifera (Lamiaceae)

“…1 ) is a semideciduous shrub that is codominant in CSS habitats in southern California along with Artemisia californica Less. (Asteraceae), or California sagebrush ( Mooney, 1977 ;Westman, 1981 ). S. mellifera is one of two species of Salvia that occur at SMER and grows approximately 1 -2 m tall with infl orescences that occur on determinate shoots in 1.6 -4 cm wide clusters of pale blue to lavender, two-lobed fl owers ( Hickman, 1993 ).…”

“…The California coastal sage scrub (CSS) community is found along arid slopes of coastal and interior southern California ( Mooney, 1977 ;Westman, 1981 ), and many CSS plants escape drought by dropping some or all of their leaves during the summer dry season ( Westman, 1981 ). During the rainy winter and spring months, when CSS plants develop new leaves, they exhibit high physiological rates, particularly as compared with evergreen shrubs of nearby chaparral communities ( Kolb and Davis, 1994 ).…”